Air-conditioning plants or packs of the above described general type for cabin air-conditioning systems of passenger aircraft are generally known as such. They prepare and provide a stream of fresh air, to which typically a flow of so-called recirculation air is mixed, in order to adjust the temperature and the air flow velocity of the prepared mixed ventilation air in such a manner so as to achieve the greatest comfort for the occupants of the aircraft. The provision of recirculation air also reduces the required amount of fresh air or bleed air and thereby reduces the overall energy requirements. The recirculation air is typically used cabin air that is recycled and then used again. In this manner, a fresh air volume flow is constantly provided into the pressurized fuselage, while the aircraft is operating on the ground as well as during flight, so as to ensure proper ventilation of the cabin, the cockpit, the electronic bays as well as the freight compartments, and particularly to ensure a constant good air quality in the cabin and in the cockpit.
The conventional air-conditioning packs typically used for this purpose constantly develop and provide the maximum achievable cooling power or cooling capacity. Thereby, the maximum possible quantity of water is continuously removed from the air, in order to reduce or completely prevent the occurrence of icing at the outlet of the expansion turbine of the air-conditioning pack or plant. Thereby, it is possible to reduce the quantity of bleed air that must be tapped from the engine, which would appear at first to reduce the fuel consumption of the engine. Nonetheless, the disadvantage of such a conventional system is that it requires a comparatively large heat exchanger capacity in order to cool the air upstream of the expansion turbine and to remove the water that is contained in the air. The air flow resistance arising in the system due to such heat exchangers make it necessary to use a relatively high bleed air pressure to achieve an adequate air flow, which in turn requires relatively high engine rotational speeds or requires the bleed air to be tapped from a higher compressor stage, i.e. a compressor stage having higher pressure, of the engine. This in turn ultimately leads to an increase in the fuel consumption. Considered alternatively, if the fuel consumption is maintained the same, then a comparatively small fresh air quantity would be available for use in the air-conditioning system. In any event, there is a disadvantageous balance between the fuel consumption and the available fresh air quantity.